Reclaiming lubricants



Patented Jan. 18, 1944 RECLAIMING LUBRICANTS August H. Riesmeyer, Arnold, Pa assignor to Aluminum Company of America,-Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application June'Z'l, 1940, Serial No. 342,695

4 Claims. (Cl. 19616) This invention relates to the reclamation of metal working lubricants, and particularly to the reclamation'of lubricants used in the working of light metals, aluminum and magnesium, by the removal of contaminating substances to make the lubricants suitable for further use in metal working processes.

While lubricants are used in many types of cold working processes in the fabrication of aluminum and magnesium products, they are used most extensively in rolling aluminum and magnesium sheet, strip, and foil products, and for this reason the present invention is described in connection with the reclamation of lubricants used in the rolling process, though it is apparent that the invention can be advantageously employed in the reclamation of lubricants used in otherfabrication processes employed with these materials.

The lubricants used in the rolling of light metals perform several functions. They appear to help the passage of the metal through the rolls, permitting relatively high gauge reductions in the individual roll passes. They also perform the function of reducing the heat generated in the rolling process both by reducing the friction and by their action as a coolant. Obviously, to obtain any appreciable cooling, the lubricants must be supplied in rather large quantities. Another important function of these lubricants is the protection which they afford the metal against marring and scratching when'the metal is stacked or coiled subsequent to the rolling operation.

The principal lubricants which have been used in the rolling of light metals are well refined mineral oils varying from 45 seconds to 1000 seconds Universal Saybolt viscosity. Lubricants of this character can be used alone, but generally they are provided with from 1 to 20 per cent of various modifying agents. Specifically, these modifying agents are usually selected from the group consisting of the fixed oils or fats such as palm oil, cocoanut oil, cotton seed oil, peanut oil, sperm oil, fish oil, spermaceti, tallow, lard fat, and horse fat, or mixtures of these materials.

The mills used in the' rolling of light metals are usually provided with circulating systems to feed the lubricants to the entry side of the rolls, and the systems are adapted to recirculate the excess oil., After a relatively short period of use, the

lubricants become contaminated and rendered fluences which make the lubricant unsuitable for further use. Probably the principal contaminating substances in 'oil which has been used in these processes are the oxidation products of the oil itself, solid carbonaceous matter formed by the partial decomposition of the oil, pa'rticles'of the metal being worked, and oxidationproduc'ts of the metal being worked.

It has been found economically unfeasible to reclaim these contaminated lubricants by means of any of the presently knownmech'anical separation processes, such a's'sedimentation and decantation, filtering, or centrifuging. This diificulty probably arises from thefact that many of the contaminating substances pre'sent'are extremely fine, being substantially colloidal in nature, and apparently will pass through even the finest filtering media which canbe'p'r'actically used. The larger particles can be removed'by various mechanical separating processes, -but the removal of these larger particles does not render the lubricant fit for reuse in fabrication processes. Among'the principal contaminating substances which are not removed by the usual mechanical separating processes appear to be extremely finely divided particles of the metal or of the oxide of the metal, together with finely divided carbonaceous matter.

marking or'marring'of the surface and frequently, in the case of rolling'thin'nietal foil, actually result in perforation of the material produced. Another-defect caused in light metal products is the staining of the product during heat treatment due to the burning onto the'surface of the solid residue of the contaminated lubricant. Stains formed'in this manner are practically impossible to remove and render thematerial in whicht'hey appear commercially unacceptable;

The present invention is predicated uponthe discovery that these contaminating substances can be removed from the lubricantby treating the lubricant with ce'rtainreagents'which'will either combine with themetal'or the oxide of the metal being worked in-the fabrication process, forming salts or compounds which'can be subsequently readily removed from the lubricant,

or which, when present in the lubricant, do not impair its characteristicsand render it satisfactory for reuse in" metal fabrication processes. The amounts of these reagents usedmay be computed in terms of the metallic content of the contaminated lubricant, and when so employed, these reagents appear to dissolve or otherwise to make it possible to remove all of those contaminating substances present in the lubricant that make it unfit for further use in metal working processes.

The specific reagents which have been found to effect a satisfactory reclamation of these contaminated lubricants are sulphuric and hydrochloric acids. That these reagents could be satisfactorily used in the reclamation of 'suchlubricants is directly contrary to the opinion generally held in the metal working artswhere it has-been believed that the contact of refinedlubricants with strong mineral acids should be avoided under all circumstances. The presence in a lubricant of strong mineral acids, even in relatively minute amounts, leads to the rapid deterioration of the equipment with which it is used, particularly with ,finely finished equipment, such: as the=rolls.usedin the rolling ofxlight metal products. :It hasibeen discoveredthat sulphuric acid and hydrochloric acid can -be added to these lubricants in amounts effective "to-remove the contaminating substances withoutapparently increasin the corrosive vnature of *the lubricants when used :in a light metal a fabrication processes. Apparently, these reagents :combine with :the light metal and/or the oxide of thelight metal to form compounds'which caneither-be entirely removed by mechanical separation processes ror which, i if present :in :the' lubricant, do not have any deleterious effects. 'Evenif a 'slight excess of --eithe'r of these reagentsis used, as compared with the amount necessary to combine with all of the'light metal'or light metal oxide, thereuse of these lubricants in a' light metal 'formingprocess brings them :almost immediately {in contact with the "light metal being :worked, thus almost metallic impurity 'in the lubricant, permits a complete separation ,of the contaminating impurities from the lubricantwithoutin any manner impairing its suitability for reuse. *Even when added in amountsslightly'in excess of the amount which will combine with all of the. metal resent in thelubricant, the lubricant is-satisiactoryfor reuse.

It is merely necessary that "this reagent be added to the lubricant and thoroughly mixed therein and the lubricant be-allowe'd to stan'dfor a reasonably :short period of time, and apparently all of the solid contaminating substances which wouldrender thelubricant unfit for further use will settle out and the clarified lubricant can'be decanted'from a vessel'in which the materialhas been-allowed to stand. 'Asomewhat more complete recovery ofthelubricant can be obtainedby extracting it-from the residue-remaining after the decantation operation by centrifuging or filtration.

Hydrochloric acid-can be substitutedas a full =equivalentf-or 'thesulphuric acid, 'but it is not generally assatisfactory becausethe-solids usually have to be separated "from the lubricant by centrifuging or filtering" rather than'by sedimentation and decantation.

basis of the :rnetal present in the lubricant in the form of free metal and its oxide.

It is generally preferable to use these reagents in as highly concentrated form as is practical at temperatures below about C. as it has been found that highly concentrated acids are more effective and because the time required in the settling operationgfollowing the addition of the acid maybe greatly reduced. If, however, the lubricant being treated contains a large amount of 'fatty acid and it is desired to employ sulphuric acid as a reagent, it is usually advisable to use a somewhat lower concentration of sulphuricracid. -While thisiincreases the'period required toyefieot separation, there is less carbonization of-the-fatty acid witharesulting decrease in ;the fatty acid'content ofthe lubricant. It hasbeen, found that the time required to remove contaminating substances from the lubricant can be reduced in some instancestby the addition of ticularly those detergents consisting principally products of aliphatic alcohols. These additions are not necessaryto the successful operation of the-process but they do. effect a reduction inthe time required .to obtain the separation 0f :the

solid impuritiesi-rom the lubricant.

.,-The amount. of either of these-acids (HCl. and H2804) which should be added to any, given. contaminated lubricant may be determined by slowly adding the-acidto the lubricant whi-lesubjecting ,it to vigorous agitation. While undergoing this treatment, the lubricant immediately starts to lose its darkened appearance, and the :addition of ,theqacid should be discontinued as soonas the .lubricantapDears-to be completely clarified. "The ,lubricant'isthen allowed to stand for a period of time, prei'erab1y about 24-48 hours. Durin this period of standing, the compound formed,

by the light metal ,present' and the added: acid, settles tothebottom of the vesselinwhichthe lubricant has been-standing. Apparently, all of the solid matter present in the i lubricant settles out duringthis :period, and theclarified lubricant can be deoantedfrom the vessel. Thedecanted lubricant is suitable for further I use in .the rlight metal working process without any additional treatment.

As stated before, the acid'shouldbe addedin 'highly concentrated 'form as ispractical. be-

cause ,less settling time is required. Concentrations-of-sulphuric acid'varying from 50.11098 per-cent have been successfully used,'but.concentrations above per cent, suchas -oleum (fuming sulphuric acid), are not desirable.

Suitabledilution of the acid can best be obtained light metal, -,or the I sulphate of the .light metal,

as 'thecase may :be, depending .upon the (acid used, The following specific example is typical or the treatment used with a lubricant commonly employed in the rolling of aluminum.

This lubricant is specified by the suppliers as being a 45 second Pennsylvania mineral base oil having added thereto 1 per cent of horse fat and 1 per cent of sperm oil. After use for a period in an aluminum rolling process, an analysis of this oil indicated that it contained 0.028 per cent of aluminum, computed on the basis of free aluminum and its oxide. 100 gallons of this lubricant contained 0.224 pound of metallic aluminum by analysis, computed on the bases of free aluminum and its oxide. To the 100 gallon batch of the lubricant 1 pound of concentrated sulphuric acid was added. This amounted to about 85 per cent of the theoretical amount necessary to combine with the aluminum present to form aluminum sulphate. The lubricant with the acid added was agitated thoroughly for one hour at room temperature and allowed to settle for a period of 24 hours. The clarified lubricant was removed by decantation and found to be entirely suitable for reuse in the metal fabrication process in which it had been employed.

I claim:

1. The method of reclaiming lubricants consisting principally of refined mineral oils and used in the working of light metal and contain ing particles of the light metal being worked, which consists in treating the lubricant with sulphuric acid in an amount substantially equal to the stoichiometrical amount which will combine with all of the light metal present in the lubricant to form light metal sulphate, and subsequently separating the solid impurities from the lubricant.

2. The method of reclaiming lubricants consisting principally of refined mineral oils and used in the working of light metal and containing particles of the light metal being worked, which consists in treating the lubricant with sulphuric acid, in an amount substantially equal to the stoichiometrical amount which will combine with all of the light metal present in the lubricant, and alcohol to form a sulphate of the light metal, and subsequently separating the solid impurities from the lubricant.

3. The method of reclaiming lubricants consisting principally of refined mineral oils and used in the working of light metal and containing particles of the light metal being worked, which consists in treating the lubricant with sulphuric acid, in an amount substantially equal to the stoichiometrical amount which will combine with all of the light metal present in the lubricant, alcohol, and a sodium salt of a sulphuric acid reaction product of an aliphatic alcohol to form a sulphate of the light metal, and subsequently separating the solid impurities from the lubricant.

4. The method of reclaiming lubricants used in working light metals, for re-use in said working operation comprising treating a lubricant with a reagent selected from a group consisting of sulphuric acid and hydrochloric acid in an amount substantially equal to the stoichiometrical amount required to combine with all of the light metal present in the lubricant to form a salt of the light metal which is insoluble in said lubricant, and subsequently separating the solid impurities from the lubricant.

AUGUST H. RIESMEYER. 

